For many years, the issue of people being scalded by hot coffee at fast food establishments has made the headlines and the courts. Since people desire hot coffee, one solution has been to provide coffee in cups that act as thermal insulators so that the user's hand is not burnt while holding the hot cup. Styrofoam (polystyrene) is a common material used in coffee cups for this purpose. However, many people do not like polystyrene for at least two reasons. It is not biodegradable, and some of the material is ingested with the coffee. There is therefore a need for disposable cups, particularly for hot drinks, which are environmentally friendly, to replace Styrofoam disposable cups.
In the early 1990s, the Java Jacket (http://www.javajacket.com/) was introduced which is an insulating coffee cup sleeve made from waffle-textured cardboard that wraps around a standard paper cup (U.S. Pat. No. 5,425,497). Starbucks introduced a similar product and cites U.S. Pat. No. 5,205,473. Both work fairly well as long as the coffee temperature is not too hot. The materials are, of course, biodegradable.
In U.S. Pat. No. 5,222,656 Carlson introduces a design similar to 473 based on a tubular insulating sleeve from a felt-like material. The Carlson cup does not appear to have been marketed.
In U.S. Pat. No. 5,667,135 Schaefer describes a thermal insulating sleeve for drink cups made from a preform which includes a plurality of circumferentially spaced-apart rows of generally longitudinally oriented and off-set slits. The slits thereby allow the sleeve to expand circumferentially when portioned on a portion of the beverage cup side wall and, by virtue of such circumferential expansion, thereby form the insulative honeycomb structure therearound.
There are many other patents in this category that were issued despite the fact that Shikaya, U.S. Pat. No. 3,908,523, foresaw the need for such a sleeve in 1975. He describes a sleeve “disposed around the peripheral surface of the cup-like body, with the sheet member being corrugated to provide a plurality of “concavo-convex” flutes, whereby air compartments are provided between the peripheral surface of the cup-like member and the inner surface of the sheet member, comprises forming the sheet member by cutting, from a planar sheet, a planar blank having a width in excess of the peripheral length of the circular bottom of an inner cup member and a length substantially equal to the height of the side wall of the inner cup member. The opposite ends of the planar blank are then united in overlapped relation to form a circular cross-section sleeve constituting an outer member and, after such uniting, the blank is formed with “concavo-convex” flutes to form a structure whose peripheral surface is corrugated. The inner and outer members are then telescoped to form a composite liquid-tight cup with heat insulating air passages extending upwardly along the outer surface of the side wall of the inner cup member”.
However, insulating sleeves for paper cups involve maintaining inventory of an additional item for each serving and increases the cost of delivering a cup of hot drink to the customers. There is therefore a need for a sleeveless solution to delivering hot drinks to consumers.
More recently, Insulair (www.insulair.com) has essentially taken a Java Jacket and placed it between an inner and outer paper wall (U.S. Pat. No. 5,363,982). The resulting cup has the appearance of a normal paper coffee cup while providing some thermal insulation as well as being biodegradable. Yet, even Insulair's cup does not provide enough insulation, and when boiling water is poured in the cup it is too hot to handle and the hot drinks cool off too rapidly. There are three main problems with the Insulair approach. Since the corrugate is free (not adhered to the two bracing layers, or laminates) it provides none of the mechanical advantages of corrugated structures. Furthermore, the thermal insulation advantage of the “air pockets” within the corrugation channels are negated because the corrugations are vertical. In such structures, air within each channel creates heat exchanging flows (as hot air moves up and cold air down) diminishing the thermal insulating properties of air. Last, the airspace created by the corrugations is in free contact with the ambient air, which is colder than the air in said air pockets, and thus allows a process of soaking ambient air into channels and cooling the hot drinks.
In U.S. Pat. No. 5,685,480 Choi describes a disposable insulated drinking cup that includes an inner liner, an outer annular shell, and an air-filled spacer between the liner and shell. Both the corrugated wall and backing sheet are of thin-wall construction to maximize the air volume and insulation properties of the spacer. The spacer includes a corrugated wall adhered to a backing sheet, and by sealing the bottom of the structure to bottom disk, within a channel, overcomes the shortcoming of Insulair's corrugated structure. However, said channel reduces drastically the stackability of the cups (having a radius larger than the bottom radius of the external shell). Furthermore, Choi's corrugations are vertical, as are Insulair's corrugations, and thus promotes within the air channels air movement due to thermally induced differential air densities between the cold bottom of the cup and the warmer top. It should also be mentioned, that in order to practice Choi's structures, the cup's overall wall thickness is typically about 0.12 inch (0.02 inch each for the inner liner and outer shell and a radial thickness of the spacer of 0.08 inch).
There is therefore a need for a low cost insulating cup that is relatively thin, and does not rely for its thermal insulation on vertical air columns. Specifically, there is a need for a disposable and biodegradable cup that can maintain an initial thermal gradient on its wall of better than 34° F. and can maintain such a hot drink above 120° F. for more than 75 minutes. For the purpose of this specification, we define the hot pouring fluid temperature as 1920-202° F., and the “tepid temperature” under which a hot drink is no longer pleasant to consume as 120° F. We also define the hand comfort temperature, or the maximum temperature that will not cause hand discomfort as 162° F.
The present invention provides a new class of paper cups satisfying said requirements by having wall constructions providing better thermal insulation than the current state of the art and made from materials that are biodegradable and less expensive to manufacture than Insulair's cups.